Light operated guard

ABSTRACT

A light operated guard for a path which may be followed by a person or part of a person with a purpose of raising an alarm, of closing the path or stopping dangerous machinery, which utilises a modulated beam of light which traverses the said path and falls upon a photocell associated with a frequency sensitive device which acts to inhibit the raising of an alarm or the closing of the path or the stopping of the dangerous machinery or the like while the beam is uninterrupted the one to maintain a constant loop gain and the other to nullify spurious signals due to vibration and other mechanical effects due to motion of the parts of the apparatus during operation of the same.

United States Patent 119- Fuller 5] June 3, 1975 1 LIGHT OPERATED GUARD3,224,825 12/1965 Sturgis a a1. 312/223 3,640,596 2 l972 K 't 312 223[75] Inventor: Paul Fuller, Romford, England I am 2 I [73] Assignee:Roneo Vickers Limited, London, Primary Examiner lames C. MitchellEngland Attorney, Agent, or FirmWigman & Cohan 2 F] d: D 4, 1973 l 2] 57ABSTRACT [21] Appl 421719 A light operated guard for a path which may befollowed by a person or part of a person with a purpose [30] F i A li tiP i it D t of raising an alarm, of closing the path or stopping 6 1972United Kingdom llllllllllll 56370/72 dangerous machinery, which utilisesa modulated 1 beam of light which traverses the said path and falls [52]Us. CL 312/223. Zl H1 upon a photocell associated with a frequencysensitive 51 lm. A451) 77/08 device which acts ihhihh the raising of analarm 58 Field of Search 211/15 312/223 the Closing of the P thestopping 0f the dangerous machinery or the like while the beam isuninter- [56] References Cited rupted the one to maintain 'a constantloop gain and the other to nullify spurious signals due to vibrationUNITED STATES PATENTS and other mechanical effects due to motion of the21696-417 12/1954 Jouk 312/223 parts of the apparatus during operationof the same. 3,077,967 2/1963 Woodward et al. 3l2/223 X 3,181,921 5/1965Moore et al. .1 312/223 7 Claims, 2 Drawing Flgures LIGHT OPERATED GUARDThe invention relates to a light operated guard for a path which may befollowed by a person or part of a person with the purpose of raising analarm, closing the path, or stopping dangerous machinery in said pathand the like, while the object of the invention is to provide such aguard which is reliable in operation, economical to manufacture andwhich is easily adaptable to a variety of purposes.

The invention consists in a light operated guard for a path which may befollowed by a person or part of a person, with the purpose of raising analarm, of closing the path or stopping dangerous machinery in said pathand the like, comprising means for producing a beam of light, means formodulating the beam of light at a predetermined and substantiallyconstant frequency, a system of mirrors positioned adjacent boundariesof the path which cause the beam of light to be reflectec back and forthacross the path, a photo-sensitive electrical device at the end of thebeam of light remote from the means for producing a beam of light, whichprovides an electric signal of said predetermined frequency, and anelectric circuit connected to said photo-sensitive device which producesan output signal only when the light of said predetermined frequency andof a predetermined amplitude falls on the photo-sensitive device, saidoutput signal being utilised for inhibiting the raising of an alarm, theclosing of the path or stopping of dangerous machinery or the like.

The invention further consists in a light operated guard as set forth inthe preceding paragraph in which the frequency of modulation of the beamof light is greater than I cycles per second.

The invention still further consists in a light operated guard as setforth above in which the electric circuit includes a relay which closeswhile the output signal is present, and inhibits the operation of abrake upon said dangerous machinery, and on the absence of the signalallows the brake to operate upon the dangerous ma chinery.

The invention still further consists in a light operated guard as setforth above in which the means for modu lating the beam of light is aperforated disc rotated by a synchronous electric motor operated by ac.main network current.

The invention still further consists in a light operated guard as setforth above in which the electrical circuit includes a pre-amplifier,and a two-state frequency selective electronic switching device.

The invention still further consists in an automatic file storage,retrieval and replacement system utilising a lift and incorporating alight operated guard as set forth above.

The invention still further consists in an automated filing systemincorporating a lift for bringing the file to a window in the system forpresentation to an operator and returning them to their allottedpositions when required, in which the window is provided with a light operated guard as set forth above, in which the beam is reflected fromside to side of the window, and in consequence transversely of thedirection of motion of the lift, so that should an operator pass a partof his person through the window into the path traversed by the light,said part of the person is sure to be moved by the motion of the liftinto the path of said beam to interrupt the beam, if the beam has notbeen interrupted previously by the part of the person.

The accompanying drawings show, by way of example only, one embodimentof the invention when applied to an automatic file storage anddretrieval and replacement system in which,

FIG. I is a perspective view of the automatic file storage retrieval andreplacement system, showing the incorporation of the light operatedguard, while FIG. 2 shows a circuit diagram of the light operated guardwhen particularly adapted for use in a system as shown in FIG. 1.

The automated file storage system shown in FIG. I comprises a framework1, which supports shelves or runners 2, for files 3, and covered with asheet metal covering 4. The central space is provided with a liftplatform 5, which can be raised and lowered by the op erating chains 6,driven by the electric motor 7. When the controls, (not shown), areoperated, the platform 5 is raised or lowered as the case may be to thelevel of the tile required, thereupon the file 3 is pulled onto theplatform 5 by the magnetic means 8, which is movable automatically intocontact with the required file 3 and the file is then pulled on to thelift platform 5. The magnet of the magnetic means is energisedautomatically as and when required.

The front of the storage system is provided with a window 9 by way ofwhich the file may be withdrawn from the platform 5. In FIG. 1 theplatform 5 is shown halfway down the window, and the file of coursecannot be withdrawn until it has reached the bottom of said window,where it automatically stops. It will be apparent that it is extremelydangerous to pass an arm through the window, while the lift patform isin motion, seeing that it is possible for the arm to be trapped eitheragainst the upper or lower extremities of the window, either by a fileor by the empty lift. In consequence, the storage system is providedwith a light operated guard to immediately stop the lift if this shouldhappen, and for this purpose, there is provided a long box likestructure 10, 11, on each side of the window 9.

The box 11 has five apertures therein, behind the top one 12 of which isprovided an electric lamp, with suitable optical system for providing anarrow beam of light, and a synchronous electric motor driving aperforated disc which modulates the beam emerging from the aperture 12.The box 10 has four corresponding apertures behind each of which ispositioned a mirror which reflects the beam across the opening. Theapertures 13, 14 and 15 in box 11 also have mirrors positioned behindthem. The mirrors are adjustable as to the angle they present to thebeam, so that it is finally projected upon the photo-sensitiveelectrical device behind the bottom aperture in box 11.

Although paths of the beam back and forth across the window 9 areclosely spaced, should a hand or an object be inserted between the beamsit will be pushed by the motion of the moving platform 5 into the pathof a beam. The beam will then be interrupted and the lift motor 7immediately de-energised and a brake, (not shown), applied to stop theplatform 5. If the hand or object is then removed, the lift platform 5is inhibited from further motion until the apparatus is switched off andthe controls are re-set.

FIG. 2 shows a circuit diagram of the essential parts of the electricalcircuit operating the guard, in which the principal components arehoused for protection in a casing represented by the dashed line 16which is housed in the box 11. This is provided with a plug and socketconnector 17 with terminals A K, which is connected by leads to thethree units, 18, 19 and 20, housed in the filing system itself. Seeingthat the circuit in the casing 16 is an inhibiting unit, the liftplatform will not move if the plug and socket connector 17 is separated.Only while the circuit in the casing 16 is operating in the requiredmanner, will the lift work.

The three units l8, l9 and 20 comprise a power supply unit operated fromthe main current supply network and providing current for motor M andthe transformer T at main supply voltage and the remainder of theapparatus at 26v do The unit 19 is a control logic for inhibiting theoperation of the lift motor in the absence of the current from theelectronic circuit by way of the terminal E. The unit 20 is an emergencybrake logic operated when the contacts 26 and 27 of the relay RL open.by way of the terminals H and K.

As may been seen from FIG. 2, the lamp L is operated by the transformerT and may be a 6 volt watt quartz iodide lamp, the primary of thetransformer T being connected in parallel with the motor M and suppliedwith current at the main network supply voltage by way of terminals Aand B.

The electronic circuit is supplied with 26 volts d.c. between theterminal C and the earth terminal D, when it is divided to supply therelay RL and transistor TR2 direct and by way of the resistor R1 tosupply the transistor TRl and the unit FX301. The resistor R1 acts as acurrent limiting resistor for the zener diode Z. The fixed resistor R2in series with the variable resistors R3 and R5 provide an adjustablebias for the transistor amplifier TR] and hence the switching thresholdof transistor amplifier TRl. R4 is a current limiting resistor, and R6is the collector load resistor for the transistor amplifier TRl.

The photo-sensitive device P.V.C. is a large area, red sensitivephotovoltaic cell. It is preferable to provide a red filter in the pathof the beam emerging from the top aperture of the box 11 to avoidunpleasant effects upon the operator as would be the case if a whitelight is used. and that is why a red sensitive photovoltaic cell ispreferred.

The unit marked FX301 is a commercially available unit from ConsumerMicrocircuits Limited, and comprises a high performance microcircuitwhich functions as a frequency operated switch providing two states, theone when the input signal corresponds in frequency to that to which theunit is adjusted, and the other state when the signal is interrupted orvaries in frequency from that to which the unit is adjusted. Resistor R7is a current limiting resistor for the unit FX301, while resistor R8 isa current limiting resistor for transistor TR2. The zener diode providesa stable volts supply for the unit FX301.

The transistor TR1 amplifies the signal from the photo-cell P.\".C. tothe level required for introduction to the unit FX301, and is fed by wayof the capacitor C1 and resistor R7 to the terminal 1 thereof. The diodeD1 is provided as a requirement of the manufacturers of the unit FX301.Capacitor 02 connected to terminal 2 of the unit FX301 controls theoperating time of the circuit which is approximately 10 milliseconds.excluding the relay RL. The terminals 3, 6 and 9 are connected to the 15volt d.c. line, while the terminal 4 is the output from the unit and isconnected to the transistor TR2 by way of the current limiting resistorR8. Terminal 7 is earthed.

Resistors R9, R10, R11 and R12 are chosen of such values as to providesuitable switching threshold of the unit FX301. The switching point withthe values of these resistors and the capacitors C3 and C4 may beadjusted by means of the variable resistors R11 and R12 between 800 c/sand 1.2 Kc/s. From these figures it can be realised that in this form ofconstruction it is preferred to arrange for the modulation frequency tobe in the neighbourhood of 1000 c/s. The relay RL is a volt do. two polechangeover relay which acts as one of the final control elements, andthe contacts of which are used depends upon the purpose to which theguard is being put. The diode D2 is provided to suppress high voltagespikes due to the presence of the relay coil damaging the transistorsand the unit FX301.

The modulator is interposed between the lamp and lens system, and ispreferably in the form of a perforated aluminium disc with holes equallyspaced around its periphery. The disc rotates at approximately 2,800r.p.m. and is driven by a low power shaded pole motor. The light beam ismodulated at a frequency of approximately 1 Kc/s. As the system is onlyresponsive to light modulated at the predetermined frequency, it is notaffected by sunlight or other unmodulated light or modulated light ofany frequency other than the chosen fre quency falling on the photocell.

It will be seen from FIG. 1 that the top and bottom paths of the lightbeam are at right angles to the boxes 10 and 11, as this preventsapertures being available for access without operation of the device.

The use of a light guard as opposed to a mechanical shutter offers theadvantage of at least a 20 percent decrease in the total operating time.

Besides providing a signal for inhibiting the motion of dangerousmachinery, the system may be used to ring an alarm if the beam is causedto cross back and forth across an opening through which a person canwalk, thus preventing a burglar entering a prohibited area, or it can beused to close a shutter or other obstruction to the entry of aprohibited area. In the latter case the contacts 26 and 27 may be closedas the device operates to ring the alarm or close the shutter. Also, thepath followed by the beam may be different from that shown in FIG. 1,and the light source may be at the bottom and photocell at the top, oralternatively the beam may be reflected from top to bottom and back orat an angle and so on.

One purpose of the modulation of the beam is to prevent the apparatusfrom being rendered inoperative by the introduction of an externalsource of light not hav ing the precise frequency of modulation of thebeam of the apparatus. Also, the modulation of the beam allows one touse an a.c. amplifier and thus produce considerable amplificationwithout difficulty, and without loss of stability, thereby avoidinginherent disadvantages such as drift of do. amplifiers. The higher thefrequency at which the light is modulated the greater is thediscrimination possible by the electronic means, and differentiation inrespect of a light of constant amplitude falling on the photocell.

Other means of modulating the light may be used but the method preferredis the most economical and reliable method found. It is preferred to usea shaded pole motor as the speed of rotation is substantially constantwith frequency, and therefore may be said to be synchronous with themain supply frequency.

A quartz iodide lamp is preferred as it gives high luminosity and longlife.

Although the circuit illustrated is preferred as it simplifies themethod of construction and therefore reduces the cost of manufacture,other circuits having the same characteristics may be used and mayinclude an amplifier of a conventional type which includes frequencysensitive selecting means to inhibit the amplifier if the modulationfrequency should vary from the desired frequency or should be reduced tosuch an extent as to prevent proper operation of the amplifier.

It is preferred to operate the modulation at a frequency greater than100 cycles per second so as to avoid interference by the artificialillumination of a room in which the apparatus is housed. It is alsopreferable not to use a multiple of the frequency of the main supplyfrequency as thereby it would be possible to prevent the apparatus fromworking by shining a light into the photocell operated from the mainsupply at a frequency by which is a multiple of the main supplyfrequency. By varying the number of apertures in the modulating disc itis possible to operate the devices at different frequencies so thatguards in different establishments may operate at different frequenciesand therefore make it more difficult for the operation of the apparatusto be interfered with.

The electric circuit is so arranged that if any of the circuits areinterrupted or any of the apparatus interfered with by breaking acircuit or temporarily interrupting the main supply the operation of thelift is interfered with and the apparatus cannot be reinstated into theoperative state until all the circuits are completed and the main supplyconnection finally made.

The 26 volts d.c. supply is derived from the power supply unit viainhibit control logic 19 with the object of incorporating a delay, toallow the modulator motor to attain full speed and the lamp to attainfull brightness. A further inhibit facility is carried out by theinhibit control logic 19 to enable the operator to remove items from theprohibited area without operating the brake, and thus rendering themachine immobile. This is provided through terminals D and E.

It is to be understood that the above description is by way of exampleonly, and that details for carrying the invention into effect may bevaried without departing from the scope of the invention.

I claim:

1. A light operated guard for a path which may be traversed by a personor part of a person, for the purpose of raising an alarm, closing thepath or stopping dangerous machinery or the like in said path,comprising means for producing a beam of light, means for modulating thebeam of light at a predetermined and substantially constant frequency, asystem of mirrors positioned adjacent boundaries of the path forreflecting the beam of light back and forth across the path, aphoto-sensitive electrical device at the end of the beam of light remotefrom the means for producing a beam of light for generating an electricsignal of said prede termined frequency, and an electric circuitconnected to said photo-sensitive device for producing an output signalresponsive to said electric signal only when the light of saidpredetermined frequency and of a predetermined amplitude falls on saidphoto-sensitive device, said electric circuit including means activatedby said output signal for inhibiting the raising of an alarm. theclosing of the path or stopping of dangerous machinery or the like,whereby interruption of said beam of light will prevent production ofsaid output signal therebyprecluding activation of said inhibitingmeans.

2. A light operated guard as claimed in claim 1, including means formodulating the beam of light at a frequency greater than lOO cycles persecond.

3. A light operated guard as claimed in claim 1 in which the electriccircuit includes a relay adapted to close during production of saidoutput signal thereby inhibiting the operation of a brake upon saiddangerous machinery, and adapted to open on the absence of said outputsignal thereby allowing the brake to operate upon the dangerousmachinery.

4. A light operated guard as claimed in claim 1 in which the means formodulating the beam of light is a perforated disc rotated by asynchronous electric motor operated by ac main supply network current.

5. A light operated guard as claimed in claim 1 in which the electriccircuit includes a pre-amplifier, and a two-state frequency selectiveelectronic switching de vice.

6. An automatic file storage, retrieval and replacement system utilisinga lift and incorporating a light operated guard as claimed in claim 1.

7. An automated filing system incorporating a lift movable along a pathfor bringing a file to a window in the system for presentation to anoperator and returning the file to its allotted position when required,wherein the window is provided with a light operated guard as claimed inclaim 1 in which the beam is reflected from side to side of the windowtransversely of the direction of motion of the lift along said path,whereby in the event an operator should pass a part of his personthrough the window into the path traversed by the beam, said part of theperson will be moved by the lift into the path of said beam by themotion of the lift, to interrupt the beam, if the beam has not beeninterrupted previously by the part of the person.

1. A light operated guard for a path which may be traversed by a personor part of a person, for the purpose of raising an alarm, closing thepath or stopping dangerous machinery or the like in said path,comprising means for producing a beam of light, means for modulating thebeam of light at a predetermined and substantially constant frequency, asystem of mirrors positioned adjacent boundaries of the path forreflecting the beam of light back and forth across the path, aphoto-sensitive electrical device at the end of the beam of light remotefrom the means for producing a beam of light for generating an electricsignal of said predetermined frequency, and an electric circuitconnected to said photo-sensitive device for producing an output signalresponsive to said electric signal only when the light of saidpredetermined frequency and of a predetermined amplitude falls on saidphoto-sensitive device, said electric circuit including means activatedby said output signal for inhibiting the raising of an alarm, theclosing of the path or stopping of dangerous machinery or the like,whereby interruption of said beam of light will prevent production ofsaid output signal thereby precluding activation of said inhibitingmeans.
 1. A light operated guard for a path which may be traversed by aperson or part of a person, for the purpose of raising an alarm, closingthe path or stopping dangerous machinery or the like in said path,comprising means for producing a beam of light, means for modulating thebeam of light at a predetermined and substantially constant frequency, asystem of mirrors positioned adjacent boundaries of the path forreflecting the beam of light back and forth across the path, aphoto-sensitive electrical device at the end of the beam of light remotefrom the means for producing a beam of light for generating an electricsignal of said predetermined frequency, and an electric circuitconnected to said photo-sensitive device for producing an output signalresponsive to said electric signal only when the light of saidpredetermined frequency and of a predetermined amplitude falls on saidphoto-sensitive device, said electric circuit including means activatedby said output signal for inhibiting the raising of an alarm, theclosing of the path or stopping of dangerous machinery or the like,whereby interruption of said beam of light will prevent production ofsaid output signal thereby precluding activation of said inhibitingmeans.
 2. A light operated guard as claimed in claim 1, including meansfor modulating the beam of light at a frequency greater than 100 cyclesper second.
 3. A light operated guard as claimed in claim 1 in which theelectric circuit includes a relay adapted to close during production ofsaid output signal thereby inhibiting the operation of a brake upon saiddangerous machinery, and adapted to open on the absence of said outputsignal thereby allowing the brake to operate upon the dangerousmachinery.
 4. A light operated guard as claimed in claim 1 in which themeans for modulating the beam of light is a perforated disc rotated by asynchronous electric motor operated by a.c. main supply network current.5. A light operated guard as claimed in claim 1 in which the electriccircuit includes a pre-amplifier, and a two-state frequency selectiveelectronic switching device.
 6. An automatic file storage, retrieval andreplacement system utilising a lift and incorporating a light operatedguard as claimed in claim 1.